guardian
Well-Known Member
Yep, for secondary bonding to polyester - epoxy all the way!
Polyester vs Epoxy Resin?
- Thread starter Tim Good
- Start date
Yep, for secondary bonding to polyester - epoxy all the way!
coopec
N/A
CSM hasn't got much strength. It is good for mold work: I made up dorade boxes using a female mold and CSM. But I wanted strength for my propeller tube and also rudder stock tube. I was going to use PVC tube as a former but found to my surprise that PVC tube is not a uniform diameter. I finished up wrapping baking paper (parchment paper) around the cutlass bearing (secured with cellotape) then laid up over that using WR/Epoxy. It worked fine. (The walls of the tubes are around ½ in. thick)
Regarding powder bound CSM that is a new one on me. I wondered why I hadn't heard of it but then found
"There are some places that sell chopped strand mat that is compatible with epoxy but it is hard to come by and much more expensive". I can find only one crowd that sells it in Australia. Maybe common in the UK?
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Javelin
Well-Known Member
Don't know who told you csm isn't strong.
Woven is stronger but only in the specific directions of weave bias, off bias its weaker.
CSM is a lot better at bonding to old grp and wood than woven.
Peeling off a woven repair from old grp is easy, get a chisel under an edge and it'll just peel off.
CSM is a lot harder to remove.
Most of my repairs use an initial couple of layers of csm before I add biaxial making sure I get the orientation right.
I have a full roll here of 250g powder bound csm, whilst laminating its not as robust as the styrene based csm and you have to be quite gentle with it.
The biggest issue is wetting out by hand using epoxy, you either have to run with small pre-heated batches or use the special low viscosity epoxy.
Woven is stronger but only in the specific directions of weave bias, off bias its weaker.
CSM is a lot better at bonding to old grp and wood than woven.
Peeling off a woven repair from old grp is easy, get a chisel under an edge and it'll just peel off.
CSM is a lot harder to remove.
Most of my repairs use an initial couple of layers of csm before I add biaxial making sure I get the orientation right.
I have a full roll here of 250g powder bound csm, whilst laminating its not as robust as the styrene based csm and you have to be quite gentle with it.
The biggest issue is wetting out by hand using epoxy, you either have to run with small pre-heated batches or use the special low viscosity epoxy.
Ric
Well-Known Member
If you have a proper AWB (not a manky OWB - "off-white boat") then white Milliput is absolutely brilliant for small gelcoat repairs. It is water soluble (until hardened) so can be smoothed by finger and water.
For bigger jobs, as somebody else wrote, epoxy resins are not great when mixed with glass fibre mat - much better to use polyester resin for that. So better to have an emergency repair kit of polyester resin and fibre mat. Generally polyester fillers are better for small hull repairs as they are far nicer to smooth and sand down.
I have found epoxy fillers are better for fairing down a cast iron keel (if you have one). But they are a devil to sand down and so you have to get them very smooth before they set. They really do stick well to prepared cast iron though. My 20 year old cast iron keel is lovely and smooth, but hate to think what it would look like without all the care and attention.
For bigger jobs, as somebody else wrote, epoxy resins are not great when mixed with glass fibre mat - much better to use polyester resin for that. So better to have an emergency repair kit of polyester resin and fibre mat. Generally polyester fillers are better for small hull repairs as they are far nicer to smooth and sand down.
I have found epoxy fillers are better for fairing down a cast iron keel (if you have one). But they are a devil to sand down and so you have to get them very smooth before they set. They really do stick well to prepared cast iron though. My 20 year old cast iron keel is lovely and smooth, but hate to think what it would look like without all the care and attention.
coopec
N/A
I'm not sure why you are suggesting Woven Roving is "stronger but only in the specific directions of weave bias". The strands are woven like a wicker basket i.e. at 90° to each other. What is the direction of bias? (There is a multi axial material and a unidirectional which complicates things)
View attachment 69895
Choosing Between Fiberglass Cloth and Chopped Strand Mat (fiberglass mat)
https://fiberglasswarehouse.com/choosing_which_fiberglass/
"Chopped strand mat is the least expensive fiberglass and is often used in mold construction or projects where thickness is needed. Mat is often used as the first layer (before the gelcoat) in a laminate to prevent print through. Print through is when the fabric weave texture shows through the resin.
Chopped Strand mat does not have much strength. If you need strength you should choose a woven cloth or you could mix the two. Mat can be used between layers of woven fabric to help build thickness quickly and aid in all layers bonding well together."
Javelin
Well-Known Member
I think we are at odds about the word strength.
I am referring to the strength of bond.
Strength to weight is another matter and not really relevant to this thread.
In a real life, on board scenario you will usually need bonding strength for repairs as a priority, as form strength can be built up with additional layers.
Whether you chose to believe me or not, csm has a stronger bond to old grp laminate than woven.
Remembering that the first layer is the most important on any repair.
Bulkhead and knee tabbing is more likely to delaminate if the initial layer was woven (unless vacuumed but not many folk carry this kit on board)
When replacing chain plate knees, skin fitting pads, bulkhead tabbing and the like its always been easier to remove old layers if they had just used woven.
Often the only way to remove csm is to grind it away.
There are exceptions and I'm finding that if the hull was infusion molded and then the builder laminated knees and brackets on later during the build the bonding strength appears to be weaker.
This maybe due to bad keying or differences in styrene expulsion levels compared to a traditional layup resin, given that build times are much reduced these days.
I work with polyester and epoxy almost every day. (for example my current two projects are fitting a bowthruster in a Bav and peeling and epoxying a Sadler 34)
I carry both polyester and epoxy on board my boat.
With polyester I can laminate a pad, a stay on a rudder post, a broken engine bearer, a broken washboard, a snapped tiller or pole and have it cured in less than a couple of hours, which will get me home.
When I get home I would probably redo a repair using epoxy.
I am referring to the strength of bond.
Strength to weight is another matter and not really relevant to this thread.
In a real life, on board scenario you will usually need bonding strength for repairs as a priority, as form strength can be built up with additional layers.
Whether you chose to believe me or not, csm has a stronger bond to old grp laminate than woven.
Remembering that the first layer is the most important on any repair.
Bulkhead and knee tabbing is more likely to delaminate if the initial layer was woven (unless vacuumed but not many folk carry this kit on board)
When replacing chain plate knees, skin fitting pads, bulkhead tabbing and the like its always been easier to remove old layers if they had just used woven.
Often the only way to remove csm is to grind it away.
There are exceptions and I'm finding that if the hull was infusion molded and then the builder laminated knees and brackets on later during the build the bonding strength appears to be weaker.
This maybe due to bad keying or differences in styrene expulsion levels compared to a traditional layup resin, given that build times are much reduced these days.
I work with polyester and epoxy almost every day. (for example my current two projects are fitting a bowthruster in a Bav and peeling and epoxying a Sadler 34)
I carry both polyester and epoxy on board my boat.
With polyester I can laminate a pad, a stay on a rudder post, a broken engine bearer, a broken washboard, a snapped tiller or pole and have it cured in less than a couple of hours, which will get me home.
When I get home I would probably redo a repair using epoxy.
coopec
N/A
"I think we are at odds about the word strength" AGREED
"Remembering that the first layer is the most important on any repair" AGREED.
That is why you never lay-up WR on top of WR. Always WR/CSM/WR for the reason you stated.
I think another reason we appear to disagree is the weight of WR. When I laid up my hull I used quite heavy WR (600 gm m2) and each layer was interspersed with a layer of CSM. Being the hull the areas being fiber-glassed were quite flat and had no sharp corners.
If I was fiber-glassing in the bulkheads using polyester I would use CSM (I used that on my yacht) But maybe I could use a light weight WR as it is very flexible but I wonder what I would gain?
You'd agree with me that if we were looking at doing a repair then we'd have to assess the problem and pick the appropriate materials. That could be CSM or WR then we'd have to pick the appropriate weight and also decide on epoxy or polyester. No one way fits all.............
Cheers
"Remembering that the first layer is the most important on any repair" AGREED.
That is why you never lay-up WR on top of WR. Always WR/CSM/WR for the reason you stated.
I think another reason we appear to disagree is the weight of WR. When I laid up my hull I used quite heavy WR (600 gm m2) and each layer was interspersed with a layer of CSM. Being the hull the areas being fiber-glassed were quite flat and had no sharp corners.
If I was fiber-glassing in the bulkheads using polyester I would use CSM (I used that on my yacht) But maybe I could use a light weight WR as it is very flexible but I wonder what I would gain?
You'd agree with me that if we were looking at doing a repair then we'd have to assess the problem and pick the appropriate materials. That could be CSM or WR then we'd have to pick the appropriate weight and also decide on epoxy or polyester. No one way fits all.............
Cheers
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Rikds
Well-Known Member
Biax and epoxy is my favourite combination for almost everything. I question the comments about CSM bonding better. The bond is entirely down to surface preparation and the chosen resin. Epoxy bonds best to most substrates.
One of the properties of CSM (and why it is layered between woven cloth) is it improves interlaminate shear strength. However this mainly applies to polyester as epoxy is tougher and stronger than polyester.
That's just my view, apparently I can be wrong!
One of the properties of CSM (and why it is layered between woven cloth) is it improves interlaminate shear strength. However this mainly applies to polyester as epoxy is tougher and stronger than polyester.
That's just my view, apparently I can be wrong!